Thomas á Kempis. The imitation of Christ. Book 2, chapter 6.

Of the joy of a good conscience

The glory of a good person is the testimony of a good conscience. Therefore, keep your conscience good and you will always enjoy happiness, for a good conscience can bear a great deal and can bring joy even in the midst of adversity. But an evil conscience is ever restive and fearful. Sweet shall be your rest if your heart does not reproach you. Do not rejoice unless you have done well. […] Whoever minds neither praise nor blame possesses great peace of heart and, if their conscience is good, they will easily be contented and at peace. Praise adds nothing to your holiness, nor does blame take anything from it. You are what you are, and you cannot be said to be better than you are in God's sight. If you consider well what you are within, you will not care what others say about you. They look to appearances but God looks to the heart. They consider the deed but God weighs the motive.

A humble soul always does good and thinks little of itself. It is a mark of great purity and deep faith to look for no consolation in created things. Those who desire no justification from without have clearly entrusted themselves to God: "For no one who commends themself is approved," says St. Paul, "but whomever God commends" (2 Cor. 10:18).